Server recording and client playback of computer network characteristics

ABSTRACT

A system and a method for server recording and client playback of computer network characteristics. In general, the network simulation system includes a recording module residing on a server that records and stores the network characteristics in a data collector file. The system also includes a playback module residing on a client that plays back the data collector file upon request. The data collector file includes a log file, which is used to store initial request data, and a data file, which is used to store other data. The method of the invention includes recording computer network characteristics on a recording server and playing back the recording on a client to the same or another server. The recording method uses a global filter residing on the server to record the network characteristics. The playback method plays back the data collector file to simulate the characteristics of real-world network sessions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 09/461,900, entitled “Server Recording and ClientPlayback of Computer Network Characteristics,” filed Dec. 15, 1999, nowU.S. Pat. No. 7,013,251, the entire contents of which are herebyincorporated by reference.

BACKGROUND

Capacity planning of a server used in a server/client wide-area network(WAN) is quickly becoming more important as the use of WANs (such as theInternet) rapidly increase. WAN servers often are used by Internet sitesand must be able to efficiently handle the anticipated requests to thesite. Capacity planning helps predict if and when system saturation willoccur by testing the maximum user load and speed of the target server.Thus, accurate and realistic testing a server is a crucial foundationfor building a network system.

A common approach to testing a server is to perform browser or clientrecording of a browser session. Recording of a browser session generallyinvolves starting a browser session and making requests to a server. Allof the outgoing HyperText Transfer Protocol (HTTP) messages are recordedand the status of the request and the contents of what was requestedwill be displayed. One problem, however, with client recording of abrowser session is that it does not accurately simulate the real-worldcase where a plurality of clients are sending requests to the server.Although several copies of the single browser session may be played backsimultaneously to simulate a plurality of clients, this can lead to ashut down of the operating system due to thread limitations well beforea realistic number of clients can be simulated. More importantly, thetiming of a client recorded single browser session is not accurate orrealistic because only copies of a single browser session are beingplayed back. In addition, critical server information such as the numberof open sockets, when the sockets are closed, the state of a request(i.e., where a HTTP server is with regard to processing the request),when the HTTP server began to process the request and information andpossible storage of a request that caused the server or HTTP service toshutdown prior to request processing are not available. Thus, clientrecording completely fails to capture a great deal of serverinformation, including the important server information listed above.

SUMMARY

The invention disclosed herein includes a system and method forrecording and playing back computer network characteristics. Inparticular, the invention records the network characteristics on aserver and plays back the recorded characteristics on a client. Thisarrangement provides accurate and realistic simulation of computernetwork characteristics that can be used for a variety of purposes (suchas capacity planning and network troubleshooting). The invention allowsthe recorded characteristics to be scaled to provide intensive testingof the capacity and resource limits of a network server. Further, theinvention permits a recording server to record multiple clients andplayback that recording on a single machine (in order to simulatemultiple clients).

The invention also provides a record of network characteristics that arenot captured in server log files (such as bad requests from a client).The invention collects more accurately the network characteristics beingreceive by a server and provides more data on these networkcharacteristics than other systems and techniques. This networkcharacteristics data may be used, for example, to analyze customer usagepatterns and the flow of requests to a network system (such as a WorldWide Web site). By providing server recording of networkcharacteristics, the invention provides more accurate, detailed andrealistic simulation of a real-world network and captures a greateramount of data than other systems and techniques (such as those systemsand techniques that record on a client).

The system of the invention generally includes a recording module thatresides on a server and records and stores the network characteristicsassociated with networks sessions in a data collector file. A playbackmodule that resides on a client receives the data collector file andplays back the data collector file upon request. The data collectorfile, which may be played back faster or slower to simulate moreintensive or less intensive network session characteristics, includes alog file and a data file. The log file is used to store headerinformation received from a client during recording and the data file isused to store other data. The recording module also includes aregistration module, for registering the recording module with theserver operating system, a tracking module, for tracking users, and alog restriction/rolling module for taking action to prevent the recordeddata from filling the available storage space on a server. Inparticular, log rolling allows a user to preserve data by movingcaptured data to another machine without any loss of current data beingreceived by the server.

The invention also includes a method for recording computer networkcharacteristics on a server and playing back those characteristics on aclient. The recording method of the invention includes using a globalfilter residing on the server to record the network characteristics.Recorded information is stored in a data collector file that includes alog file and a data file. The playback method includes receiving a datacollector file containing recorded network characteristics and playingback the data collector file to simulate the characteristics of areal-world network session. Further, the playback method includesvarying, the playback speed and multiplying the number of recorded users(or repeating the same recording a number of times if only one user wasrecorded) to vary the intensity of the recorded network characteristics.

Other aspects and advantages of the invention as well as a more completeunderstanding thereof will become apparent from the following detaileddescription, taken in conjunction with the accompanying drawings,illustrating by way of example the principles of the invention.Moreover, it is intended that the scope of the invention be limited bythe claims and not by the preceding summary or the following detaileddescription.

DRAWINGS DESCRIPTION

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a block diagram illustrating an apparatus for carrying out theinvention.

FIG. 2 is an overall block diagram of two computer networksincorporating the network simulation system of the invention.

FIG. 3 is a general block-flow diagram illustrating the networksimulation system shown in FIG. 2.

FIG. 4 is a detailed block diagram illustrating the record module of thenetwork simulation system shown in FIG. 3.

FIG. 5 is a block diagram illustrating an example implementation of theglobal filter shown in FIG. 4.

FIG. 6 is a detailed flow diagram of the operation of the record moduleshown in FIG. 4.

FIG. 7 is a detailed block diagram illustrating the playback module ofthe network simulation system shown in FIG. 3.

FIG. 8 is a detailed flow diagram of the operation of the playbackmodule shown in FIG. 7.

DETAILED DESCRIPTION

In the following description of the invention, reference is made to theaccompanying drawings, which form a part thereof, and in which is shownby way of illustration a specific example whereby the invention may bepracticed. It is to be understood that other embodiments may be utilizedand structural changes may be made without departing from the scope ofthe invention.

I. Introduction

The invention described herein includes a system and method forrecording computer network characteristics of network sessions on aserver and playing back the recording on a single client machine orseveral client machines. Unlike existing network simulation systems thatuse manufactured static scripts that are continuously looped, theinvention provides an actual real-world dynamic recording of networksessions in a production environment that may be played back in acontrolled test environment. The invention accurately simulates thechaos and other characteristics that are present in real-world networksessions and provides a more detailed and realistic simulation in whichto test a server.

II. Exemplary Operating Environment

FIG. 1 and the following discussion are intended to provide a brief,general description of a suitable computing environment in which theinvention may be implemented. Although not required, the invention willbe described in the general context of computer-executable instructions,such as program modules, being executed by a computer. Generally,program modules include routines, programs, objects, components, datastructures, etc. that perform particular tasks or implement particularabstract data types. Moreover, those skilled in the art will appreciatethat the invention may be practiced with a variety of computer systemconfigurations, including personal computers, server computers,hand-held devices, multiprocessor systems, microprocessor-based orprogrammable consumer electronics, network PCs, minicomputers, mainframecomputers, and the like. The invention may also be practiced indistributed computing environments where tasks are performed by remoteprocessing devices that are linked through a communications network. Ina distributed computing environment, program modules may be located onboth local and remote computer storage media including memory storagedevices.

With reference to FIG. 1, an exemplary system for implementing theinvention includes a general-purpose computing device in the form of aconventional personal computer 100, including a processing unit 102, asystem memory 104, and a system bus 106 that couples various systemcomponents including the system memory 104 to the processing unit 102.The system bus 106 may be any of several types of bus structuresincluding a memory bus or memory controller, a peripheral bus, and alocal bus using any of a variety of bus architectures. The system memoryincludes read only memory (ROM) 110 and random access memory (RAM) 112.A basic input/output system (BIOS) 114, containing the basic routinesthat help to transfer information between elements within the personalcomputer 100, such as during start-up, is stored in ROM 110. Thepersonal computer 100 further includes a hard disk drive 116 for readingfrom and writing to a hard disk, not shown, a magnetic disk drive 118for reading from or writing to a removable magnetic disk 120, and anoptical disk drive 122 for reading from or writing to a removableoptical disk 124 such as a CD-ROM or other optical media. The hard diskdrive 116, magnetic disk drive 128 and optical disk drive 122 areconnected to the system bus 106 by a hard disk drive interface 126, amagnetic disk drive interface 128 and an optical disk drive interface130, respectively. The drives and their associated computer-readablemedia provide nonvolatile storage of computer readable instructions,data structures, program modules and other data for the personalcomputer 100.

Although the exemplary environment described herein employs a hard disk,a removable magnetic disk 120 and a removable optical disk 124, itshould be appreciated by those skilled in the art that other types ofcomputer readable media that can store data that is accessible by acomputer, such as magnetic cassettes, flash memory cards, digital videodisks, Bernoulli cartridges, random access memories (RAMs), read-onlymemories (ROMs), and the like, may also be used in the exemplaryoperating environment.

A number of program modules may be stored on the hard disk, magneticdisk 120, optical disk 124, ROM 110 or RAM 112, including an operatingsystem 132, one or more application programs 134, other program modules136 and program data 138. A user (not shown) may enter commands andinformation into the personal computer 100 through input devices such asa keyboard 140 and a pointing device 142. Other input devices (notshown) including, for example, a microphone, joystick, game pad,satellite dish, camera, scanner, or the like may be connected to thepersonal computer 100. These other input devices are often connected tothe processing unit 102 through a serial port interface 144 that iscoupled to the system bus 106, but may be connected by other interfaces,such as a parallel port, a game port or a universal serial bus (USB). Amonitor 146 or other type of display device is also connected to thesystem bus 106 via an interface, such as a video adapter 148. Inaddition to the monitor 146, personal computers typically include otherperipheral output devices (not shown), such as speakers and printers.

The personal computer 100 may operate in a networked environment usinglogical connections to one or more remote computers, such as a remotecomputer 150. The remote computer 150 may be another personal computer,a server, a router, a network PC, a peer device or other common networknode, and typically includes many or all of the elements described aboverelative to the personal computer 100, although only a memory storagedevice 152 has been illustrated in FIG. 1. The logical connectionsdepicted in FIG. 1 include a local area network (LAN) 154 and a widearea network (WAN) 156. Such networking environments are commonplace inoffices, enterprise-wide computer networks, intranets and the Internet.

When used in a LAN networking environment, the personal computer 100 isconnected to the local network 154 through a network interface oradapter 158. When used in a WAN networking environment, the personalcomputer 100 typically includes a modem 160 or other means forestablishing communications over the wide area network 156, such as theInternet. The modem 160, which may be internal or external, is connectedto the system bus 106 via the serial port interface 144. In a networkedenvironment, program modules depicted relative to the personal computer100, or portions thereof, may be stored in the remote memory storagedevice 152. It will be appreciated that the network connections shownare exemplary and other means of establishing a communications linkbetween the computers may be used.

III. General Overview

As shown in FIGS. 2-8 for the purposes of illustration, the inventionmay be embodied in a system and a method for a system for recordingnetwork sessions on a server and playing back the recording on a clientmachine. The recording includes detailed information about the networksession (such as timing, user and socket information) that provides anaccurate and realistic network simulation that is not available withsimulation systems that use client recording and manufactured staticscripts. The dynamic real-world recording of network sessions created bythe invention may be played back in a controlled testing environment totest, for example, the capacity and performance of a server prior to itsactual deployment in a production environment.

In addition to capacity planning, the invention has other uses andapplications in a networking environment. By way of example and notlimitation, the invention may be used to test an operating system (suchas Internet Information Server (IIS)). This testing may be performed byinstalling the invention on a server, recording data and playing backthe recorded data to reproduce any errors encountered. The invention mayalso be used to ensure that a new version of an operating system willoperate properly prior to actual use. This would provide a customer witha confidence that the customer's network would run smoothly using thenew version. For example, if a customer is using version 3.0 of anoperating system and would like to upgrade to version 5.0, the inventionmay be used to record live requests on the customer's network that isrunning version 3.0, setup a mirrored network that is running version5.0, and playback the recording on the mirrored network to verify thatversion 5.0 would be stable (and be, for example, faster with bettermemory management). The invention may also be used to migrate a userfrom one operating system to another using a technique similar to thetechnique mentioned above. Moreover, the invention may be used to stresstest a network so that the capabilities and limits of a network systemmay be determined.

The data files created by the record module of the invention may also beused to perform detailed analysis. Because the data files created by therecord module capture detailed information about the network (such asnetwork traffic), significant aggregate information may be gained byanalyzing these data files.

FIG. 2 is an overall block diagram of two computer networksincorporating the network simulation system 200 of the invention. Thecomputer networks illustrated are only examples of several types ofcomputer networks that could incorporate the network simulation systemof the invention. In general, the network simulation system of theinvention includes both recording on a server and a playback on aclient.

In one embodiment, server recording occurs in a production environmenton a wide area network (WAN) 204. The WAN 204 includes a recordingserver 208 having server operating system and connected to a network 216via a network connection 224. In a production environment, real networksessions and requests arriving at the recording server 208 may berecorded. A plurality of WAN client machines (or clients) 232 are alsoconnected to the network 216 via their respective network connections240. At any given time, the number of WAN clients 232 connected to therecording server 208 over the network 216 may vary. For example, therecording server 208 may be a Web server that has users accessing thesite over the Internet. The number of users accessing the site may rangefrom zero to the maximum number of connections that the Web server canaccommodate.

Server recording in the invention is performed by a record module 244.The record module 244 resides on the recording server 208 and recordsrequests transmitted by a WAN client 232 to the recording server 208.These requests generally are to access a page contained on the recordingserver 208. In general, the record module 244 records request made bythe WAN client 232 and stores these requests in a data collector file.

In one embodiment, client playback of a recording made by the recordingserver 208 occurs in a test environment on a local area network (LAN)248. The LAN 248 includes a testing server (a server being tested) 256that is in network communication with LAN clients 264. In a testenvironment, the realistic simulation provided by the network simulationsystem 200 may be used to test and tune the testing server 256 toachieve optimal performance prior to introducing the testing server 256into a production environment. Moreover, the network simulation system200 may be used to test additional software that runs on the testingserver 256 or custom applications written for the testing server 256.Although three LAN clients 264 are illustrated, the number of LAN clientmay be one or more. A playback machine 272 is in communication with theLAN clients 264. The playback machine 272 may be one of the LAN clients264 or a separate machine having a processor.

A playback module 280 resides on the playback machine 272 and performsthe playback of a recording made by the record module 244 of theinvention. In particular, the playback module 280 reads individualrecords from a data collector file (containing requests recorded by therecord module 244) and sends these records to the LAN clients 264. Asexplained in detail below, each individual record is assigned to a LANclient 264. Each LAN client 264 then transmits a recorded request to thetesting server 256, thereby realistically and accurately simulating aproduction environment. In addition, each LAN client 264 is capable ofplaying back a recording made by the record module 244 that includes,for example, requests from multiple LAN client 264. Thus, each LANclient 264 is capable of simulating multiple recorded client duringplayback.

FIG. 3 is a general block-flow diagram illustrating the networksimulation system shown in FIG. 2. In general, network simulation systemrecords network requests to a server within a production environment,stores the requests in memory and plays the recorded requests back on aclient in a testing environment. Specifically, the network simulationsystem 200 of the invention includes a recording server 208 and a datacollector file 308 within a production environment 316. In oneembodiment, the production environment is one in which the recordingserver 208 receives real-world requests from a plurality of outsideusers. Although in one embodiment the recording server is in aproduction environment and records real-world requests, alternateembodiments may be implemented.

The network simulation system 200 of the invention also includes aplayback machine 272, reading data recorded by the recording server 208,at least one client 264, for sending requests to a testing server 256,and the testing server 256, for processing the requests sent by theclient 264. These machines occupy a testing environment 348 whereby thetesting server 256 may be tested and evaluated. The data (such asperformance and capacity data) collected during the simulation testingof the testing server 256 may be sent for further processing andinterpretation (box 356).

The record module 244 resides on the recording server 208 and recordsrequests that are received by the recording server 208 (box 364). Theserequests are stored (box 372) by the record module 244 in the datacollector file 308. The playback module 280, which resides on theplayback machine 272, read individual records (box 380) from the datacollector file 308 and sends each record (box 388) to at least oneclient 264. The client 264 sends the requests (box 396) to the testingserver 256, which receives and processes the incoming requests (box398).

IV. System and Operational Details

As discussed above, the network simulation system of the inventionincludes a record module, for recording network sessions on a recordingserver, and a playback module, for playing back the recording on aclient. The structure and operation of each of these modules will now bediscussed. Although the network simulation system of the invention willbe described as containing multiple modules, other embodiments arepossible that implement the described functionality of the inventiondifferently. By way of example and not limitation, these differencesinclude having a different number of modules, having a differentarrangement of modules and having different modules than those described(including having a single, monolithic module having the functionalityof all the modules).

Record Module

Structural Overview

FIG. 4 is a detailed block diagram illustrating the record module of thenetwork simulation system shown in FIG. 3. Generally, the record module244 records requests received by the server on which the record module244 resides and stores these requests along with other information. Therecord module 244 includes a global filter 400 that captures datareceived by the server. The global filter 400 is notified of certainevents by the server operating system (such as Internet InformationServer (IIS)). For example, the server operating system listens for arequest to be received and, when it occurs, the global filter 400 isnotified and begins capturing the data from a host environment. A hostenvironment can be, for example, an operating system, a networkoperating system, an application designed to run on top of an operatingsystem, a technology that is part of an operating system (such as IIS)and a group of technologies on the computer.

In order to be notified of these events the record module 244 mustregister with the server operating system. The record module 244includes a registration module 410 that registers with the serveroperating system and informs the operating system for which events tonotify the record module 244. Further, the record module 244 includes acaching module 420 that caches the data sent by the global filter 400. Atracking module 430, which is also included in the record module 244,tracks specific network information that is needed by the networksimulation system and that the user may desire to track. For example,the tracking module 430 is capable of keeping track of which client senta certain request and at what time the request was received by theserver.

Another module included in the record module 244 is a logrestriction/rolling module 440, which is capable of limiting the size ofthe file that stores the recorded data. The log restriction/rollingmodule 440 achieves this by either deleting the file or moving the datato another machine to preserve captured information. The record module244 also includes a controller 450, for processing and providing controlto the record module 244, and a data collector file 460, for storing thedata collected by the global filter 400. The data collector file 460includes a log file 470, for storing header and tracking information,and a data file 480, for storing other types of data.

FIG. 5 is a block diagram illustrating an example implementation of theglobal filter shown in FIG. 4. In particular, the global filter 400 isshown implemented into the server operating system on the recordingserver 208. The global filter 400 is implemented between a port handlingmodule 500 of the server operating system, which scans a port 510 forincoming requests, and a processing module 520 of the server operatingsystem. In order to capture raw data from the port 510, the filtershould be global. Other types of non-global filters may be used on a persite basis. For example, if there are multiple sites residing on therecording server 208 then multiple non-global filters may be set up foreach site. However, the global filter 400 must also be used because itcaptures requests for all sites residing on the recording server 208.This feature is desirable because all of the requests received by therecording server 208, regardless of the site being requested, should berecorded.

Operational Overview

FIG. 6 is a detailed flow diagram of the operation of the record moduleshown in FIG. 4. Prior to receiving data from the recording server, therecord module must register with the server operating system (box 600).As described below in a working example, there are several notificationsthat the record module can receive from the server operating system. Asa request arrives at the recording server, the server operating systemnotifies the record module that there is a request incoming (box 610).The global filter then captures raw data being received by the recordingserver over the port.

The record module queries a high-performance hardware counter (such as ahigh-resolution system clock) that has a resolution at least in thepico-seconds range. This type of hardware counter is found frequently onnewer computers. This hardware counter is used to order the raw datawithin the log file by time-stamping precisely when the raw data wasreceived by the record module.

The record module then begins to cache the raw data from the request(box 620). Memory is allocated to create a cache and headers of therequest are cached. In general, header information from the request isto be written to the log file while the body of the request is writtento the data file without being cached. A header can be a unit ofinformation that precedes a data object (such as is in the body of therequest). However, there is the possibility that the full request willnot be sent as a single unit by the server operating system, and theentire request may be received in several units spread over time.Although most requests will be a manageable size (such as a few hundredbytes), other requests may be larger and the operating system may not beable to send all the packets of the entire request together. Moreover,the recording server may have other priorities with other clients (suchas uploading a large file) and this may cause the request to be sent tothe record module in several portions. When a request is received inseveral portions, it is possible that each portion will have a headersection. Further, the body of the request, when it is transmitted, mayalso arrive in multiple portions, and each portion of the body iswritten directly to the data file. The request is cached until all theheaders for that request are received in order to separate the headersection from the body of the request, piece the header back together andwrite the header information to the log file and the data within thebody of the request to the data file. Thus, the request is cached untilthe end of the headers is reached.

The headers are cached for at least two reasons. First, the invention iscapable of determining whether the request is a duplicate request (asoften happens during a Windows® NT® LAN Manager (NTLM) typeauthentication. Second, the invention is capable of ensuring thatinformation used to uniquely identify a user (discussed below) iscompletely in memory.

A determination of whether the end of headers has been reached is made(box 630). If all of the headers have not been received, then the recordmodule continues caching the request (box 640). If all of the headersfrom the request have been received, the record module pieces the headerinformation together and writes that information into the log file (box650).

Immediately after all of the headers have been received the recordmodule searches for a special “cookie.” In general, a cookie can be asmall text file that can contain information or a small piece ofinformation about the client, its user and the user's preferences. Thecookie that the record module searches for is a special cookie that wasplaced there by the record module in order to identify a user makingmultiple requests to the server. Each cookie contains at least a uniquevalue (such as a globally unique identifier (GUID)) to provideidentification for the user. If the cookie does not exist in the requestthen a unique value is assigned to the cookie and the unique value isstored as part of the request in the log file. If the request includes acookie, the unique value corresponding to the cookie is located and theunique value is stored as part of the request in the log file. This ishow the recording module tracks users.

When the recording server sends back a response to the requesting clientthe cookie is also returned with instructions to include the cookie withsubsequent requests. The requesting client then knows that it must senda cookie every time it makes a request to the recording server. Further,an expiration time may be set on the cookie so that the cookie will lastonly as long as the user is logged on.

One advantage of tracking users in this manner is that recording can bedone across a network cluster. In other words, users can be trackedacross a cluster of multiple recording servers. If, for example, duringa user's set of transactions, the user's requests are moved or forwardedto multiple recording servers the unique value assigned to the user willpermit the multiple recording servers to record and uniquely identifythe user. After recording, postprocessing can be performed on the logfile of each of the multiple recording servers in the cluster togenerate a single log file containing all of the requests made by aspecific user in chronological order. Alternatively, instead of creatinga single log file the log files of the multiple recording servers may bemerged during playback by the playback module.

The recording module also keeps track of whether the request is from anew socket or an open socket. A socket can be a software object thatconnects an application to a network protocol. For example, a browsercan open a socket that enables it to send and receive messages byreading and writing data to and from the socket. A global socket counteris maintained and every time a request is made the global socket counteris advanced. In addition, a per socket request counter is maintained sothat during playback the order and socket that the request was receivedon can be determined. Thus, the per socket request counter tracks andlogs the socket number and the number of times that particular sockethas been accessed. Further, when a socket is closed the socket numberand the unique value associated with that socket number are tracked andlogged along with the time.

Another feature of the recording module is that a server status code istracked for each request. When the server status code cannot bedetermined (such as during the writing of the body of the request to thedata file) a status value (such as −1) is entered in the server statuscode field. When the correct server status code becomes available thestatus value is overwritten by the correct server status code. Thisfeature is useful for troubleshooting the network. For example, if theserver operating system fails unexpectedly the request that caused thefailure can be found by searching the log file for the status value. Theearliest request that has a status value written in the server statuscode field is likely the request that caused the failure, and at aminimum indicates the area where the request that caused the errorresides.

Once all of the headers have been received the record module then beginswriting the body of request and other incoming data from that request tothe data file (box 660). The record module then determines if all of thedata from the request has been received (box 670). If not, then thefurther incoming data is written to the data file. Otherwise, the recordfor that request is closed within the data file (box 680).

An optional feature that may be included on the record module is logfile rolling and termination. Recording of the requests being receivedby the recording server can occupy large amounts of memory and canimpose serious burdens on the memory storage capabilities of therecording server. The log restriction/rolling module 440 provides anoption to the user that allows the user to specify a time limit and asize limit on the data collector file to preserve memory resources. Thefile may either be deleted or closed and moved to another storage area(such as another machine or another hard drive).

Playback Module

Structural Overview

In general, the playback of the invention plays back on a client machinea recording made on a recording server. The playback module allows asingle client to simulate multiple clients by playing back a recordingof multiple client on the single client. Further, the requests containedon the recording may be “time-compressed” so that playback speed isincreased. Speeding up playback may be used to stress the server beingtested and determine its limits.

FIG. 7 is a detailed block diagram illustrating the playback module ofthe network simulation system shown in FIG. 3. The data collector file460, which includes the log file 470 (containing header and trackinginformation) and the data file 480 (containing request data), isaccessed by a data collector file reader 700. The data collector filereader 700 is a tool that reads a single record from the data collectorfile 460 and passes the record to a controller 710. The controller 710includes a controller mapping table 720 to determine which client shouldbe sent a specific request. As noted above, using the network simulationsystem of the invention a single client can simulate multiple users.

The controller 710 sends requests to the client 264 until the requestcache 730 of the client 264 is either filled or the controller 710 runsout of data. In addition, a client mapping table 740 is maintained onthe client 264 for use in determining when a user has not made a requestfor a period of time. This information may be used to time out a user inorder to free the resources used by the client machine in simulatingthat user. Timing out a user can mean that the user is removed from alist (such as a mapping table) after a period of inactivity. Both thecontroller mapping table and the client mapping table are in oneembodiment hash tables that contain the necessary mapping information.

Operational Overview

FIG. 8 is a detailed flow diagram of the operation of the playbackmodule shown in FIG. 7. At the start of playback (box 800) the datacollector file reader 700 begins reading a single record from the datacollector file 460 (box 810). The playback module 280 then determines,by reading the unique value (such as a GUID) which user sent the requestcontained in the record. When the user is established, the playbackmodule 280 determines whether the user is in the controller mappingtable 720 (box 820).

The controller mapping table 720 maps a user to a client machine. Thisis necessary to avoid the situation where more than one machine isplaying back requests from the same user. For example, many HTTP serverskeep state information on users (based on some cookie value) thusnecessitating that recordings made by the invention be played back onthe same client machine. The controller mapping table 720, which in oneembodiment is a hash table, takes into account the number of clientmachines available and then generates a table that assigns a clientmachine to a particular user. All requests from this user are sent tothat specific client machine. One advantage this feature provides isautomatic load balancing between the client machines. This allowsplayback to be more efficient and improves the fidelity of the playbackto the original recording.

If the user is not in the controller mapping table 720, the playbackmodule 280 assigns the user to a client machine (box 830). An entry inthe controller mapping table 720 is then created that maps the user totheir associated client machine (box 840). After a user mapping ispresent the controller mapping table 720 is used to map the user to theassociated client machine (box 850). The controller 710 sends the recordto the request cache 730 of the client 264 (box 860) and keeps adding tothe request cache 730 of the client 264 even while the client 264 isplaying back. After receiving a notification to start from thecontroller 710 the client 264 begins sending request to the testingserver 256. After the client has played back the data in the requestcache 730 the data may either be discarded or overwritten by incomingdata. When the end of the data collector file 460 is reached thecontroller 710 sends out an end of data file message to the clients.

Users who have not made a request for a period of time (or users whohave “timed out”) are determined dynamically by the playback module 280.In particular, the controller 710 examines the client mapping table 740at a regular interval to determine whether a request has been made by auser within the time period. The client mapping table 740, which in oneembodiment is a hash table, maps a user to the time the last request wasmade by that user. Using the client mapping table 740, the playbackmodule 280 can determine whether the user has made a request during atime period. If not, then the user is deleted from system. This featureincreases system performance and preserves client resources. Inaddition, it is more efficient to keep track of users who have timed outon the client machines rather than the server, because the server is notslowed down and it is less costly to acquire more clients rather thanservers.

The playback module 280 also closes sockets when instructed to by thedata collector file 460. Although socket closure is tracked by therecording server 208 and not determined dynamically during playback, anytime a notification of socket closure that was recorded on the recordingserver 208 is received by the playback module 280 that socket is closed.

V. Working Example

The following working example is only one exemplary illustration of howthe invention may be implemented. Those skilled in the art willrecognize that several other implementations of the invention arepossible. In this working example, the system and method of theinvention uses a global filter to record request received by an InternetInformation Server (IIS) server and play the recording back against thesame or another IIS server. The global filter is capable of recording arequest from any IP address and any virtual directory to the IIS server.

In this working example, an Internet Server Application ProgramInterface (ISAPI) global filter was used on a recording server to recordnetwork characteristics. The ISAPI global filter was implemented intoIIS between the IIS port handling and the IIS processing layers. Thefilter registered as a medium with IIS so that the filter got calledafter any ISAPI dynamic link libraries (DLLs) that were registered as ahigh. For requests received, objects registered as a high get calledfirst by IIS, then those registered as medium are called, and so on. Forrequest being sent out the objects are called in reverse order. Oneexample of an ISAPI DLL that may register as a high is SSL. Byregistering as a medium with IIS the ISAPI global filter of theinvention received the raw data after SSL had decrypted the data.

When the ISAPI global filter registered itself with IIS, severalfeatures were enabled so that IIS notified the filter upon theoccurrence of certain events. In this example, the filter registered tobe notified whether the request came from a secure or non-secure port.Requests from a non-secure port have a certain port number associatedwith the request. Similarly, requests from a secure port (such as aSecure Socket Layer (SSL) or a Secure HyperText Transfer Protocol(S-HTTP) request) have another number associated with them. The filteralso registered to be notified when raw data arrived at a port (eithersecure or non-secure). Because of the way the ISAPI global filter wasimplemented into IIS the ISAPI global filter actually got called beforeIIS began processing the data. This feature can be useful fortroubleshooting the network because by examining the log file it can bedetermined at what time a network problem occurred and what request mayhave caused the network problem.

The ISAPI global filter also registered with IIS to be notified ofserver status codes, socket terminations, socket that were being openedand port numbers. When a request was received by IIS, the ISAPI globalfilter was notified and given the raw data from the port. The requestwas then cached until all of the header information was received. Thenthe header information was written to the log file. When all of theheaders were received, the header information was time-stamped andwritten to the log file. The time stamps were relative to when IISstarted. In addition, port number, socket number, client IP address andthe server status code were also written to the log file.

After all the headers were received, the remainder of the incoming datawas written to the data collector file. Two files were created: the logfile, which holds the initial (or header) request data, and the datafile, which holds any data beyond the initial request data. The formatof the log file included the port the request was received on and theuser identification. The user identification is a GUID that uniquelydefines the user. In addition, the log file included the server IPaddress, the socket number the request as received on, theidentification of the request made on a socket, the time the request wasreceived and the server status code.

The body offset value (in relation to the rest of the request) was alsowritten in the log file. If the body offset is a non-zero value thisindicates that the data was received in more that one portion. The bodyoffset is written at the end of the data and contains the offset to thenext portion of data. The body offset is used so that if additional dataassociated with a certain request is received after the data is writtenit can be easily appended. In addition, during playback the datacollector file reader can go easily piece together sections of databelonging to the same user. The data file format also includes an offsetvalue and is written in a similar manner. When the recording wasfinished both the log and data files were closed and were ready forplayback on a client machine.

The foregoing description of the invention has been presented for thepurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. It is intended that the scope of the invention be limited notby this detailed description of the invention, but rather by the claimsappended hereto.

1. A computer-implemented method for simulating network characteristics,comprising using the computer to: implement a filter into an operatingsystem of a server; capture network data from a host environment usingthe filter; record network characteristics using a record modulecontaining the filter that resides on the server; store the recordednetwork characteristics in a data collector file for playback on aplayback machine; and simulate the network characteristics using therecorded network characteristics.
 2. The computer-implemented method ofclaim 1 wherein the filter is a global filter.
 3. A computer-implementedmethod for simulating network characteristics, comprising using thecomputer to: record network characteristics from a network session usinga filter that resides on a server; store the recorded networkcharacteristics in a data collector file for playback on a playbackmachine; limit a size of the data collector file that stores therecorded network characteristics by using a log restriction/rollingmodule; and play back at least some of the recorded networkcharacteristics faster or slower than the network characteristics wereoriginally recorded to simulate different intensity levels of therecorded network characteristics.
 4. The computer-implemented method ofclaim 3, further comprising using a computer to limit the size of thedata collector file by at least one of: (a) using the computer to deleteat least a portion of the data collector file; (b) using the computer tomove at least a portion of the data collector file to another machine.5. The computer-implemented method of claim 3, wherein the datacollector file comprises a log file, which stores header and trackinginformation, and a data file, which stores other types of data.
 6. Thecomputer-implemented method of claim 5, further comprising using thecomputer to cache at least a portion of incoming network data andsubsequently using the computer to write the cached data to the logfile.
 7. The computer-implemented method of claim 1 further comprisingusing the computer to play back the recorded network characteristics toa testing server, wherein the playback machine is a client.
 8. Thecomputer-implemented method of claim 7, further comprising using thecomputer to play back the recorded network characteristics to a testingserver, wherein the playback machine is a client.
 9. Thecomputer-implemented method of claim 7, further comprising using thecomputer to read at least a portion of the recorded networkcharacteristics stored in the data collector file.
 10. Thecomputer-implemented method of claim 1, wherein the network datacomprises header data and body data, and the data collector filecomprises a log file, which stores the header data, and a data file,which stores the body data.
 11. The computer-implemented method of claim1, further comprising using the computer to track network informationfrom the recording server.
 12. The computer-implemented method of claim3, wherein the playback machine is a client machine.
 13. Acomputer-implemented method for simulating network characteristics,comprising using a computer to perform: a recording step for recordingcharacteristics from a network session using a filter that resides on aserver; a storing step for storing the recorded network characteristicsin a data collector file for playback on a playback machine; a sizelimitation step for limiting a size of the data collector file thatstores the recorded network characteristics by using a logrestriction/rolling module; and a playback step for playing back therecorded network characteristics faster or slower than the networkcharacteristics were originally recorded using a playback moduleresiding on the playback machine to simulate different intensity levelsof the recorded network characteristics.
 14. The computer-implementedmethod of claim 13, further comprising: a first data collection step forstoring header data in a log file; and a second data collection step forstoring body data in a data file, wherein the log file and the data fileare part of a data collector file for storing the recorded networkcharacteristics.
 15. The computer-implemented method of claim 13,further comprising a generation step for generating a custom-generatedlog file that stores the recorded network characteristics, wherein thecustom-generated log file is not a server log file of the server.